Quantum confinement of electrons in clean nanowires and nanofilms results in the formationrnof a series of subbands that move in energy with changing wire/film thickness.rnWhen the bottom of such a subband moves through the Fermi surface, the density ofrnstates changes and a size-dependent superconducting resonance appears, leading tornquantum-size oscillations in the critical temperature Tc and the order parameter 4rn. Our theoretical formulation is based on a numerical solution of the BogoliubovdernGennes equations in the clean limit